In June 2022, the US Occupational Safety and Health Administration (OSHA) issued an “Advance Notice of Proposed Rule Making (ANPRM)—Blood Lead Level for Medical Removal” in which the agency sought input on reducing the current blood lead level (BLL) triggers in the medical surveillance and medical removal protection (MRP) provisions of the general industry and construction standards for lead.1 These lead standards had last been updated in 1978 and 1992, respectively. In response, the American College of Occupational and Environmental Medicine (ACOEM) provided written comments to the OSHA Lead Docket (No. OSHA-2018-0004) on October 28, 2022. The comments, developed by an ACOEM working group, reinforced and expanded on ACOEM's 2016 Workplace Lead Exposure position statement.2
ACOEM believes that multiple, high-quality, prospective cohort studies linking lead exposure to an increased risk of cardiovascular and cerebrovascular disease mortality necessitate that mandatory MRP benefits be instituted for a single BLL ≥30 μg/dL or for two successive BLL ≥20 μg/dL measured at a 4-week interval. The goal of workplace lead exposure management should be to maintain workers' BLL less than 10 μg/dL (or <3.5 μg/dL in the case of women who are or may become pregnant). Because these BLL values provide at best a slim margin of safety, it would be reasonable to enact lead standards whose goal is to maintain all worker blood lead concentrations less than 5 μg/dL, or less than the US Centers for Disease Control and Prevention (CDC) blood lead reference value in the case of workers who are or may become pregnant.
ACOEM supports a reduction in the action level (AL) and the permissible exposure level (PEL) for lead in workplace air to 2 and 10 μg/m3, respectively, as 8-hour time-weighted averages (TWAs). Because exclusive reliance on airborne lead monitoring may fail to identify the severity of lead hazards in many workplaces, medical surveillance requirements of a revised lead standard should also apply to employees who perform a trigger amount of lead work based on the duration that they are engaged in altering or disturbing materials that contain lead at a concentration ≥0.5% by weight. ACOEM endorses a prominent role for physicians with requisite training and knowledge to communicate the implications of medical surveillance and blood lead monitoring directly with employees, and to institute discretionary MRP or other workplace restrictions based on the physician's evaluation of an individual worker's health and reproductive status.
Excerpts from ACOEM's October 2022 comments and recommendations to OSHA concerning revisions to the occupational lead standards are grouped under the following four subheadings3:
I. MRP benefits should be triggered at blood lead concentrations of 20 to 30 μg/dL. The goal should be to maintain all workers' blood lead concentrations less than 10 or 5 μg/dL.
ACOEM affirms the recommendation set forth in its 2016 statement on Workplace Lead Exposure that the goal of workplace protections and policies should be to maintain all workers' BLLs <10 μg/dL.2 To the extent that OSHA's question 1 in the ANPRM refers specifically to MRP benefits under the OSHA lead standards, ACOEM affirms its position that mandatory MRP should be promptly instituted for a single BLL ≥30 μg/dL or two successive BLL ≥20 μg/dL measured at a 4-week interval. This same recommendation was issued by a panel of experts in 20074 and by the California Department of Public Health.5 ACOEM emphasizes that the existence of MRP triggers at these BLLs does not indicate that health concerns and the need for lead exposure mitigation should begin at the mandatory MRP BLL. Rather, as discussed later, a series of graded educational, industrial hygiene, and medical surveillance interventions preceding mandatory MRP should be instituted at lower BLL thresholds, including discretionary MRP based on a physician's evaluation of an individual worker's health and reproductive status.
Table 2 in the OSHA ANPRM notice of June 28, 2022,1 showed that elevated lead exposure is associated with a myriad of multisystemic adverse health effects. Although it was inexplicably not cited in that table, ACOEM finds particularly compelling the epidemiological studies that establish that long-term (years to decades) exposure to blood lead concentrations in the range of 10 to 25 μg/dL substantially increase the risk of death from cardiovascular and cerebrovascular disease. The general US population experienced years to decades of BLLs that averaged in this range from the 1940s to the early 1980s.6–14 During this time, the widespread use of leaded gasoline and the common presence of lead in residential paint, soldered food, and beverage containers, and plumbing for potable water resulted in ubiquitous lead exposure. Consequently, the health effects experienced by the general population during this period have particular relevance to the risk posed by contemporary occupational exposure at similar BLLs.
Five large prospective cohort studies of individuals from the general population who lived a considerable proportion of their lives when BLLs averaged 10 to 25 μg/dL have revealed a significant association between markers of lead exposure or lead burden and cardiovascular mortality. The National Health and Nutrition Evaluation Surveys (NHANES) conducted by the National Center for Health Statistics of the CDC are large stratified, multistage probability surveys designed to select a representative sample of the civilian, noninstitutionalized US population. In 2002, Lustberg and Silbergeld15 examined the mortality experience through 1992 of adult participants in NHANES II who were 30 to 74 years of age between 1976 and 1980 and who had a baseline blood lead concentration of less than 30 μg/dL (N = 4190). After adjustment for multiple potential confounders (age, sex, location, education, race, income, smoking, body mass index, and exercise), BLLs of 20 to 29 μg/dL at baseline were associated with 39% increased mortality from circulatory disease (relative risk [RR], 1.39; 95% confidence interval [CI], 1.01–1.91), and BLLs of 10 to 19 μg/dL were associated with 10% increased mortality from circulatory disease (RR, 1.10; 95% CI, 0.85–1.43), compared with baseline BLLs less than 10 μg/dL.
A similar prospective cohort study was conducted in 2006 by Schober et al16 on a subset of participants in NHANES III who were recruited in two successive 3-year phases between 1988 and 1994. Baseline blood lead concentration was available from 9762 subjects 40 years or older. Mortality status and cause were assessed through 2000 (median length of follow-up, 8.55 years). After adjustment for multiple potential confounders including sex, race/ethnicity, education, and smoking status, Cox proportional hazards regression using age as the time scale to examine the relative hazard (RR) found that BLLs >10 μg/dL at baseline were associated with a 55% increase in mortality from cardiovascular disease (RR, 1.55; 95% CI, 1.16–2.07), and BLLs of 5 to 9 μg/dL were associated with a 20% increase in mortality (RR, 1.20; 95% CI, 0.93–1.55), compared with BLLs less than 5 μg/dL. The test for trend by BLL group was also statistically significant (P < 0.01). The group containing a baseline BLL >10 μg/dL had a median BLL of 11.8 μg/dL, with few subjects having BLL >20 μg/dL. Because of the phase out of lead in gasoline beginning in the late 1970s and the decline in BLL with reduction in all exogenous exposure, the blood lead concentrations of individuals older than 40 years at the time of their recruitment into NHANES III were likely lower than the BLLs they experienced earlier in their lives. However, because the subjects were a representative sample of the general US population, their cumulative lead exposure was strongly influenced by BLLs in the 10- to 25-μg/dL range that were typical from the 1940s to 1970s.
In 2006, Menke et al17 conducted a different Cox regression analysis of the mortality experience through 2000 of NHANES III participants older than 17 years at baseline whose blood lead concentration was less than 10 μg/dL (N = 13,946). After adjusting for multiple potential confounders, successive terciles of baseline BLLs were associated with an increased risk of death from myocardial infarction and stroke. Compared with subjects in the lowest tercile of BLL (≤1.93 μg/dL), those in the highest tercile BLL (≥3.63 μg/dL) experienced an 89% increased risk of death from myocardial infarction (RR, 1.89; 95% CI, 1.04–3.43) and a 151% increased risk of death from stroke (RR, 2.51; 95% CI, 1.20–5.26). As with the analysis by Schober et al,16 the cumulative lead exposure of the participants and likely their baseline blood lead concentration at the time of recruitment between 1988 and 1994 were strongly influenced by BLLs in the 10- to 25-μg/dL range experienced earlier in life.
Lanphear et al18 extended the analysis of Menke et al17 by reporting the cause-specific mortality experience of NHANES III participants through 2011 (N = 14,289; median, 19.3 years of follow-up). In examining the risks associated with an increase in baseline log-transformed BLL from 1.0 to 6.7 μg/dL (10th–90th percentile), after adjustment for multiple confounders, the hazard ratio (HR; RR) for cardiovascular disease mortality increased 70% (HR, 1.70; 95% CI, 1.30–2.20), and that for ischemic heart disease mortality increased by 108% (HR, 2.08; 95% CI, 1.52–2.85). When the relationship between baseline blood lead and mortality was fitted by five-knot restricted cubic splines to visualize the shape of the dose-response curve, the steepness of the relationship between blood lead and both cardiovascular mortality and ischemic heart disease mortality was steeper in subjects with a baseline blood lead <5 μg/dL than for those baseline blood lead of 5 to 10 μg/dL. In addition, the relationship between baseline blood lead and both cardiovascular mortality and ischemic heart disease mortality was greater in subjects who were younger than 50 years at baseline compared with those who were older.
Because lead accumulates in bone with a half-life of years to decades, measurement of lead in bone by noninvasive K x-ray fluorescence (KXRF) offers advantages over blood lead as a biomarker of long-term cumulative lead exposure.19 The Normative Aging Study (NAS) is a multidisciplinary longitudinal study of aging in men begun in 1963 when 2280 healthy men from the Greater Boston area between 21 and 80 years were enrolled. In the 1990s (mean, 1994 ± 3 years), KXRF measurement of lead in bone and blood lead were collected on a subset of active participants.20,21 In the fully adjusted model confined to subjects who were younger than 45 years at the time of NAS study entry (N = 637), HRs for cause-specific mortality through 2007 were assessed by tercile of patella lead concentration. Analyses were adjusted for age at KXRF measurement, smoking, and education, as well as occupation and salary and parental age and occupation at NAS study entry. Inverse probability weighting based on selected health characteristics (such as diastolic blood pressure and body mass index) were applied as an additional adjustment so that the subpopulation who participated in the KXRF measurements were representative of all NAS subjects alive at the time of the KXRF substudy enrollment. Using individuals in the lowest tercile of patella bone lead (<20 μg Pb per gram of bone mineral) as the reference group, subjects in the highest tercile of bone lead (>31 μg/g) exhibited an RR of 2.47 (95% CI, 1.23–4.96) for all cardiovascular mortality and an RR of 5.20 (95% CI, 1.61–16.8) for ischemic heart disease mortality. Blood lead, which averaged ≈5 μg/dL at the time of the KXRF substudy enrollment, was not a predictor of mortality.21 This prospective cohort study demonstrated that bone lead, a biomarker of cumulative lead exposure, was predictive of cardiovascular mortality in individuals who lived a significant proportion of their lives at a time when BLLs of 10 to 25 μg/dL were common.
Other epidemiological, clinical, and experimental studies are coherent in establishing lead exposure as a cause of death from cardiovascular disease. At low to moderate dose, lead has been demonstrated to increase blood pressure, alter cardiac conduction, increase vascular reactivity, induce oxidative stress, increase expression of proinflammatory cytokines, and alter endothelial cell function.22 Occupational cohort mortality studies have observed an increased standardized mortality rate for cardiovascular disease in lead smelter workers,23 and a significant relationship between blood lead and cardiovascular mortality within occupational cohorts assembled from large medical surveillance data sets.24,25
ACOEM considers the weight of the evidence supporting the need for revised standards to reduce occupational lead exposure and the BLLs of workers to be among the most conclusive and compelling that has ever existed for a workplace chemical regulated by OSHA. First, a key health end point of demonstrable concern is death, as compared with subtle or subclinical changes in organ function. Second, the abundant epidemiological data that support the causal relationship arise from multiple large, well-controlled, prospective cohort studies—the most rigorous and persuasive epidemiological study design. Third, causal inference is supported not only through multiple high-quality epidemiological studies that have extensively adjusted for confounders and bias, but also by numerous experimental and clinical observations that have identified plausible modes of action at consistent doses. Fourth, because cardiovascular mortality is the most prevalent cause of death in the US population, the more than 50% increase in mortality risk associated with BLLs in the range of 10 to 25 μg/dL results in a marked increase in the absolute number of deaths. Fifth, the magnitude of the cardiovascular mortality risk arising from lead exposure exceeds that of other prominent risk factors, such as smoking, elevated cholesterol, and hypertension, which have been the subject of extensive public health concern. Finally, BLLs of a magnitude linked to cardiovascular mortality remain prevalent in numerous workplaces.
ACOEM recommends that OSHA lead standards require a qualified supervising physician to review, interpret, and respond to all BLLs and other data obtained as part of workplace lead biomonitoring and medical surveillance program. As stated earlier, the goal of such a program should be to maintain all BLLs less than 10 μg/dL. Although MRP should be mandated for a single BLL ≥30 μg/dL or two BLLs at 4-week intervals ≥20 μg/dL, the supervising physician should have the independent discretion and authority to order MRP at a lower BLL based on an individual worker's medical history or health status. In revising its lead standards, OSHA should explicitly acknowledge that medical conditions, including chronic real dysfunction (serum creatinine >1.5 mg/dL for men, >1.3 mg/dL for women or proteinuria), hypertension, neurologic disorders, and cognitive dysfunction may pose a risk of material impairment of an employee's health at BLLs that chronically are ≥10 μg/dL. Accordingly, such conditions may indicate the need for physician-ordered MRP at BLLs ≥10 μg/dL or at lower BLLs based on physician discretion.4 In view of some evidence of the adverse impact of low-level prenatal lead exposure on neurodevelopment and reproductive outcome, and the absence of any identifiable BLL threshold for the deleterious effects of postnatal lead exposure on neurocognitive development,22,26 it is advisable for women who are or may become pregnant to avoid occupational lead exposure that would elevate BLL concentrations above the CDC reference value for lead (currently 3.5 μg/dL).27
Consistent with our recommendation that a qualified physician be given the discretion to order MRP or other lead exposure reduction for a worker at any BLL based on the worker's health status or condition, ACOEM further recommends that all workers eligible for biological monitoring (including BLL testing) under a revised OSHA lead standard annually complete a confidential health history form that should be forwarded to a qualified supervising physician for review. This health history form should report on health conditions, including but not limited to all of those cited in the paragraph previously, that may increase the worker's risk of material health impairment from lead exposure. In addition to reporting whether the worker is known to have hypertension, the form should also document an annual measurement of the employee's blood pressure. This health information, together with review of all biological monitoring test results, will assist the physician's determination of the need for ordering discretionary MRP or other reductions in an employee's occupational lead exposure. Physicians should be empowered to request confidential consultation, including physical examination, of any employee who completes a health history form. Employees should have the option of supplementing or revising the information provided on the annual health history form at any time for further physician review based on changes in their health status (including reproductive status).
ACOEM believes that the workplace lead exposure conditions acceptable for a worker undergoing MRP should be more protective than mere removal from work involving airborne exposure to lead at or above the AL, which is 30 μg/m3 under the current OSHA lead standards. As further explained in ACOEM's responses to OSHA's questions regarding requirements for blood lead testing and revised AL and PEL, ACOEM believes that substantial lead exposure may occur in certain job conditions or activities not subject to exceedance of an airborne AL, and that the PEL and AL should be reduced. Consistent with the recommendations of Kosnett et al,4 ACOEM believes that “removal from occupational lead exposure will usually require transfer of the individual out of any environment or task that might be expected to raise the blood lead concentration of a person not using personal protective equipment above background levels,” currently approximately 3.5 μg/dL at the 97.5th percentile. The suitability of alternative job tasks or locations at a workplace for an employee undergoing MRP could be discerned in part by the pattern of blood lead concentrations documented in other workers who engage in candidate alternative tasks or work in other locations without the use of PPE. In addition, consistent with the Cal/OSHA 2016 discussion draft lead standards pertaining to “temporary removal due to elevated blood lead levels,” MRP should result in a removal of an employee “from work having an exposure to lead at or above the AL, and from work altering or disturbing any material containing lead at a concentration equal to or greater than 0.5% by weight,”28 and additionally from work that constitutes any trigger task defined in the Cal/OSHA discussion draft for Construction.29 The rationale for these stringent criteria pertaining to suitable alternative work during MRP is to facilitate relatively rapid reduction in BLL and to reduce to the greatest extent feasible further hazardous exposure to lead.
Although the stated goal to maintain workers' BLL less than 10 μg/dL (or <3.5 μg/dL in the case of women who are or may become pregnant) is supported by extensive scientific evidence, the evidence does not establish that these same BLLs constitute thresholds below which adverse effects are unlikely to occur. Based on contemporary medical knowledge, these BLL values provide at best a slim margin of safety. It is possible that future epidemiological studies of adult populations who have seldom or never sustained BLLs greater than 10 μg/dL will detect a lead-related risk of cardiovascular morbidity and mortality, as well as other significant health effects associated with long-term exposure. The emergence of such findings will require further protective policies and regulations. A principle of regulatory toxicology and public health holds that standards governing hazardous exposures should offer a margin of safety below levels that pose a significant adverse risk to health. In issuing its 2016 final rule on occupational exposure to respirable crystalline silica, OSHA explicitly noted that it “may incorporate a margin of safety even if it theoretically regulates below the lower limit of significant risk.”30 In view of this, it would be reasonable for OSHA to enact occupational lead standards whose goal is to maintain all worker blood lead concentrations less than 5 μg/dL, or less than the CDC reference value in the case of workers who are or may become pregnant.
ACOEM believes that after MRP for an elevated blood lead concentration, return to work should be considered, based on a physician's review of the worker's health and work status, when BLL has declined to less than 15 μg/dL. BLLs assessed for the purpose of return-to-work decisions after MRP should be measured at monthly intervals. ACOEM believes that considering intraindividual and laboratory variability, a return-to-work BLL of 15 μg/dL will usually reflect a true reduction the worker's BLL. As noted in ACOEM's response to OSHA's question on MRP trigger BLLs, the physician who supervises workplace biological monitoring and medical surveillance for the worker should have the discretion, on a case-by-case basis, to continue MRP until a worker's BLL has declined to a value less than 15 μg/dL as necessary to avoid material impairment to a worker's health from lead exposure. This will include consideration of a worker's reproductive status and their ability to procreate a healthy child.
In addition, ACOEM believes that return of a worker after MRP should be predicated on the supervising physician's assessment that the conditions that resulted in MRP, including but not limited to lead exposure resulting in a BLL that may have triggered MRP, are unlikely to resume. Consistent with provisions proposed in the draft lead standards of Cal/OSHA (and a similar requirement proposed by the Washington state Division of Occupational Health and Safety),31 employers should be required to issue a “written elevated blood lead level response plan with a description of specific means that will be employed to reduce and maintain employee blood lead levels below 10 μg/dL.”28 The physician's decision to authorize return to work after MRP may be based, in part, on a review of this written plan and communication with the employer, the employer's industrial hygiene, safety, or engineering consultants, and/or the employee to assess the suitability of the response plan and its implementation.
II. The AL and PEL for lead in workplace air should be reduced from 30 and 50 μg/m3 (as an 8-hour TWA average) to 2 and 10 μg/m3, respectively.
ACOEM believes that effective worker health protection requires a reduction of the current lead standards' PEL and AL level for lead. Numerous epidemiological studies have demonstrated a significant positive relationship between airborne lead concentration and workers' blood lead concentrations. Biokinetic models based on the toxicokinetics of lead have used epidemiological data as a means of calibrating and confirming the models.32 Recently, two independently developed biokinetic models, the Leggett+ model and the DoD-O'Flaherty model, have been published to assist regulators in the identification of airborne occupational exposure limits (ie, permissible exposure limits) for lead that would maintain workers' blood lead concentration below various thresholds. The Leggett+ model,33,34 published by the California Office of Environmental Health Hazard Evaluation at the request of the California Department of Health, estimated various concentrations of lead in workplace air inhaled by workers without respiratory protection that could result in specified lead concentrations in workers' blood. Assuming 40 years of working life exposure beginning at age 25 years and a background blood lead concentration of 1.5 μg/dL, the model predicted that an 8-hour TWA PEL of 2.1 μg/m3 would result in a 95th percentile BLL of 10 μg/dL. A PEL of 10.4 μg/m3 would yield a 95th percentile BLL of 30 μg/dL.
The DoD-O'Flaherty biokinetic model,35,36 based on a model first developed by O'Flaherty, differed from the Leggett+ model by relying on somewhat different physiological assumptions and by considering the impact of a worker's birth year and accumulated lifetime lead exposure to assess the impact of adult workplace lead exposure. It predicted the blood lead distribution that would have existed in the DoD workforce on January 1, 2018, had the current DoD workforce, composed of men and women of various ages, been historically exposed full time to specified levels of airborne lead since they were 18 years of age. The DoD-O'Flaherty model related various candidate occupational exposure levels to corresponding predictions of the 95th percentile BLL. It predicted that a PEL of 3.6 μg/m3 would yield a 95th percentile blood lead concentration of 10 μg/dL.35 In a formal review of the DoD-O'Flaherty model, the National Academies of Science, Engineering, and Medicine found that the Leggett+ model and DoD-O'Flaherty model “described available BLLs with similar accuracy…. The consistency of simulated BLLs between the DoD-O'Flaherty model and Leggett+ model provided additional evidence of the reasonableness of the model inputs and assumptions.”32
The California Department of Public Health has recommended that Cal/OSHA adopt a PEL of either 0.5 or 2.1 μg/m3 to maintain workers' BLL less than 10 μg/dL.5 The Cal/OSHA discussion draft of 2016 proposed a PEL of 10 μg/m3 and an AL of 2 μg/m3.
In establishing requirements for (1) basic hygiene requirements for all workers with occupational lead exposure; (2) medical surveillance requirements (including blood lead measurements) that would be required if an AL of 2 μg/m3 were exceeded for ≥10 days per year, or irrespective of air measurements if a “trigger amount of lead work” were performed; (3) exposure monitoring at least every 12 months if the ALs were exceeded, with more frequent monitoring dependent on the magnitude exposure; and (4) a written plan for investigation and deficiency correction in the case of a blood lead ≥10 μg/dL, Cal/OSHA's discussion draft standard evinced a commitment to the goal of keeping blood lead concentrations less than 10 μg/dL for all lead workers. However, by establishing a PEL of 10 μg/m3, Cal/OSHA sought to provide employers with flexibility in the approach to maintaining all workers' BLLs below this value.
As noted in discussions held before the Cal/OSHA Advisory Meetings for Revision of the General Industry and Construction Lead Standards,28 it was recognized that the selection of PEL carries with it an implication for work that can be performed with various types of respirators based on their respective protection factors. For example, abrasive blasting of lead-coated surfaces (such as steel bridges covered with lead paint) is customarily performed by workers inside enclosures equipped with supplied air respirators with protection factors of 1000. If the PEL were 2 μg/m3, this work could be performed with a supplied air respirator only if the exposure within the enclosure were less than 2000 μg/m3. According to some stakeholder comments at meetings of the Cal/OSHA Advisory Meetings, air levels inside enclosures during abrasive blasting may sometimes be in the range of 5000 μg/m3. The selection of a PEL of 10 would allow supplied air respirators to be used inside an enclosure provided the exposure were less than 10,000 μg/m3. In similar manner, full-face respirators have a protection factor of 50. A PEL of 10 μg/m3 would allow employers to use full-face respirators in environments where air levels extended up to 500 μg/m3, instead of up to 100 μg/m3 as would be the case with a PEL of 2 μg/m3.
A Standardized Regulatory Impact Assessment (SRIA) issued by the California Department of Industrial Relations in 2020 found that Cal/OSHA's proposed revisions to the occupational lead standards were feasible and were associated with a large benefit-cost ratio.37 CDIR concluded, “As the full, long-term benefits of the proposed regulatory revisions are realized, the annual benefit-cost ratios for this regulation are quite high and sustained, with benefits expected be substantially larger than compliance costs. However, compliance costs begin to accrue immediately while the health benefits manifest themselves over time.37 The estimated aggregate breakeven point under the assumptions of this assessment would occur approximately within the first 7 years after the proposed revisions come into effect. It should also be recalled that the benefit estimates used in this study are not comprehensive and that total benefits are expected to be substantially higher.”37 According to the SRIA, if the revised lead standards were introduced in 2020, the net financial benefit by 2040 would be approximately $3,800,000,000.00 (3.8 billion dollars) unadjusted for inflation.37
ACOEM considers the Cal/OSHA proposal for a PEL of 10 μg/m3 and an AL of 2 μg/m3 to be feasible and health protective when combined with the additional provisions set forth in proposed Cal/OSHA discussion draft standards. ACOEM urges OSHA to revise its federal OSHA lead standards to include a PEL and AL at least as stringent (ie, health protective) as the Cal/OSHA proposal.
III. Instead of exclusive reliance on measurement of lead in workplace air, performance of a “trigger amount of lead work” based on the duration of time spent altering or disturbing materials that contain lead at a concentration ≥0.5% by weight should be a criterion for initiation of blood lead monitoring and medical surveillance.
ACOEM believes that OSHA should expand the criteria that mandate biological monitoring (including blood lead testing) and medical surveillance in both its general industry and construction lead standards. ACOEM endorses the expanded criteria for these programs set forth in the Cal/OSHA discussion draft standards of 2016.28 The current OSHA standard for general industry, which relies entirely on employee exposure to airborne lead at or above the current AL of 30 μg/m3 for more than 30 days per year to trigger biological monitoring, is inadequately protective of worker health for several reasons:
- As discussed further in ACOEM's response to OSHA's questions on the AL and PEL, validated biokinetic modeling and epidemiological data have established that workplace exposure to airborne lead should be considerably less than 30 μg/m3 to maintain the 95th percentile worker's blood lead concentration less than 10 μg/dL after months of steady-state exposure. In the case of the females of reproductive age, on the order of 1 month of exposure at 10 μg/m3 would likely result in the 95th percentile worker's BBL exceeding the CDC blood reference value of 3.5 μg/dL.
- Occupational health professionals have found that many lead-exposed workers have elevated BLLs even when air lead levels are below the current AL of 30 μg/m3. In such situations, lead ingestion via hand-to-mouth activity probably accounts for the exposures rather than inhalation of airborne lead. These risks can be quite significant in industries that grind, polish, or otherwise disturb lead-containing materials such as brass alloys, tin-lead solder, pottery glaze, lead weights, and bullet fragments, among others. BLLs in such workers can often exceed 10 to 20 μg/dL and may occasionally range as high as 50 to 60 μg/dL even when air lead levels are less than 30 μg/m3.
ACOEM believes that exclusive reliance on the airborne lead monitoring fails to identify the severity of lead hazards in many workplaces. California's pending rulemaking on state lead standards included a cost-benefit analysis published in 2020.37 This study, a “Standardized Regulatory Impact Analysis (SRIA),” estimated the number of employees in various industries who were likely to have significant workplace exposure to lead. Extrapolated from California to the nation as a whole, the data suggest that as many as 2 million American workers have occupational lead exposure high enough to elevate BLLs greater than 5 to 10 μg/dL. The vast majority of these workers will not currently fall under the scope of the OSHA lead standards, because in most of their workplaces, air lead levels are less than 30 μg/m3.
- 3 The current OSHA standard's exclusive reliance on exceedances of airborne lead ALs to trigger the need for blood lead testing has long been suspected to contribute to widespread undercompliance with this aspect of biological monitoring. Employers in many lead-using workplaces, especially those with relatively few employees or low to moderate exposure levels, fail to conduct air monitoring and thus never obtain evidence of AL exceedance. This was documented in 1990 by Rudolph et al38 soon after the establishment of the California Occupational Blood Lead Registry as a component of laboratory-based surveillance for occupational lead poisoning. In that study, only 2.6% of workplaces engaged in lead-using processes (employing an estimated 205,000 workers) were estimated to have ever done environmental monitoring for lead. Moreover, only 1.4% of these workplaces had routine biological monitoring programs. A study conducted by the Los Angeles County Department of Health Services in 199239 and in Ohio in 200040 also found low compliance with all lead monitoring requirements. For more than 30 years, the Occupational Lead Poisoning Prevention Program of the California Department of Health has conducted extensive education, surveillance, and outreach for primary and secondary prevention of the problem. Nevertheless, the Occupational Lead Poisoning Prevention Program continues to conclude that “many employers fail to provide BLL testing to their lead-exposed workers” and that the blood lead data reported to the state blood lead registry “likely represent a significant underestimate of the number of California workers exposed to lead.”41
- 4. Even when it is conducted, air monitoring for lead may fail to document substantial lead exposure (and hence exceedance of the airborne AL) if such monitoring is scheduled or performed in a manner that avoided places and times when peak workplace exposure occurred. In many such cases, it would be challenging for OSHA to ascertain that this may have occurred.
ACOEM endorses the approach set forth in the Cal/OSHA general industry standard discussion draft of 2016 (§5198 [j] Medical Surveillance) that would require implementation of a medical surveillance program, to include periodic blood lead monitoring, for workers exposed at or greater than an AL of 2 μg/m3 for 10 or more days per year, and for employees who perform “a trigger amount of lead work.”28 A trigger amount of lead work, which is specified in detail in §5198 (b) Definitions, is based on altering or disturbing material that contains lead at a concentration ≥0.5% by weight, or torch cutting any scrap metal. (Note: provisions are made in the discussion draft concerning the duration per month of these activities and the magnitude of BLLs that are observed in involved employees over time). ACOEM believes that the approach to require medical surveillance and blood lead monitoring on workers who alter or disturb lead containing material irrespective of airborne exposure is essential to assure adequate worker protection. In similar manner, ACOEM endorses the approach set forth in the Cal/OSHA construction standard discussion draft of 2016 that requires medical surveillance based on exceedance of an airborne AL and based on performance of various trigger tasks associated with lead exposure for a specified duration.29
IV. Physicians with requisite training and knowledge in the health hazards of lead should communicate the implications of medical surveillance and results of blood lead monitoring directly with employees. Physicians supervising medical surveillance should institute discretionary MRP or other workplace restrictions based on their evaluation of an individual worker's health and reproductive status.
ACOEM concurs with the need to revise the general industry lead standard to require that employees be notified of every BLL test result, as well as all other biological monitoring test results, within 5 days of the date that results are available from the clinical laboratory. In addition, ACOEM believes that further revisions are necessary regarding the manner in which the employee notification occurs:
A. Employee notification of the BLL results should occur in the form of a letter addressed to and sent directly to the employee from a licensed physician charged with supervising the biological monitoring and medical surveillance program conducted for lead-exposed employees. It would be acceptable for the letter to be transmitted by confidential mail or email or hand delivery at the workplace, depending on the preference identified in advance by each employee.
B. The physician should also include in the letter to the employee the following:
- Interpretative guidance concerning the BLL test results with respect to adverse health outcomes that have been associated with a range of BLL exposures
- A cumulative log of all the employee's past BLL test results
- The minimum time interval at which another BLL test should be conducted
- The physician's opinion as to whether the employee has any detected medical condition that would place the employee at increased risk of material impairment of the employee's health from exposure to lead
- Any recommended special protective measures to be provided to the employee or limitations to be placed upon the employee's exposure to lead
- Any recommended limitation upon the employee's use of respirators, including a determination of whether the employee can wear a powered air purifying respirator if a physician determines that the employee cannot wear a negative pressure respirator
- The results, along with interpretative guidance, of any other biological monitoring tests, including pregnancy or fertility tests; and medical examinations, which have been conducted as part of the medical surveillance program and biological monitoring program
- Notification of any medical condition, occupational or nonoccupational, that has become apparent to the physician as a result of review of all the employee's medical surveillance data, which dictates further medical examination or treatment
- As proposed by Cal/OSHA discussion draft general industry lead standard 2016 §5198(j)(C) (employee notification),28 a statement that the revised lead standard requires the employer to make medical examinations and consultations available, as soon as possible, upon notification by an employee either that the employee has developed signs or symptoms commonly associated with lead intoxication, that the employee desires medical advice concerning the effects of current or past exposure to lead on the employee's ability to procreate a healthy child, or that the employee has demonstrated difficulty in breathing during a respirator fit test or during use
- Updated provisions regarding medical removal protections and benefits
- A means by which the employee can confidentially contact the physician to discuss further questions or health concerns regarding occupational lead exposure
C. Upon their request, employees who participate in biological monitoring and medical surveillance conducted for lead-exposed employees should have the option of requesting that the physician letter be confidentially translated to Spanish, or such other language as may be appropriate for the employee.
ACOEM believes that the interpretation of BLLs and trends of them over time requires an understanding of the toxicology and toxicokinetics of lead in the body. Because of this complexity, the review and communication of the BLL test results and the results of other evaluations should be conducted by a physician with requisite training and knowledge regarding lead, including the adverse effects of lead and conditions predisposing to them. ACOEM believes that direct communication between the physicians who supervise the biological monitoring and medical surveillance program, and each participating employee emphasizes the medical significance and importance of these programs. Each physician engaged in the review, interpretation, and communication of biological monitoring and medical surveillance data collected in accordance with provisions of a revised OSHA lead standard should be provided access to all prior health data, lead exposure data, industrial hygiene information, restrictions and medical removal experience pertaining to the employee's lead exposure.
ACOEM believes that to assist physicians in the formulation of written communication to the employee, OSHA should issue, as an appendix to the revised lead standard or other means, recommended interpretative guidance on the relationship between blood lead, other medical tests, risks to current and future health status, and lead exposure. OSHA's suggested interpretative guidance should be updated periodically to reflect the evolving state of scientific and medical knowledge pertaining to the assessment, prevention, and management of the health effects of lead. Such interpretative guidance should be subject to expert peer review.
1. OSHA ANPR for Lead October 2022. Federal Register
2. Holland MG, Cawthon D; ACOEM Task Force on Blood Lead Levels. Workplace lead exposure. J Occup Environ Med
3. ACOEM Comments to OSHA ANPR for Lead, October 2022. Available at: https://www.regulations.gov/comment/OSHA-2018-0004-0111
. Accessed December 9, 2022.
4. Kosnett MJ, Wedeen RP, Rothenberg SJ, et al. Recommendations for medical management of adult lead exposure. Environ Health Perspect
5. Occupational Lead Poisoning Prevention Program. California Department of Public Health. In: Revising the Workplace Lead Standards: At-A-Glance
. October 2018. Available at: https://www.cdph.ca.gov/Programs/CCDPHP/DEODC/OHB/OLPPP/CDPH%20Document%20Library/LeadStdRev-At-A-Glance.pdf
. Accessed December 9, 2022.
6. Sawyer RA, Waggoner RW, Erickson AA. Statistical study of lead in human blood and urine. In: Proceedings of the Seventh Summer Conference on Spectroscopy and Its Applications Held at the Massachusetts Institute of Technology; July 17–19, 1939.
7. Robinson MJ, Karpinski FE, Brieger H. The concentration of lead in plasma, whole blood and erythrocytes of infants and children. Pediatrics
8. Hofreuter DH, Catcott EJ, Keenan RG, Xintaras C. The public health significance of atmospheric lead. Arch Environ Health
9. Working Group on Lead Contamination. Survey of Lead in the Atmosphere of Three Urban Communities
. Cincinnati, OH. No. 999-AP-12: Public Health Service, DHEW; 1965.
10. Goldwater LJ, Hoover AW. An international study of “normal” levels of lead in blood and urine. Arch Environ Health
11. Thomas HV, Milmore BK, Heidbreder GA, Kogan BA. Blood lead of persons living near freeways. Arch Environ Health
12. Environmental Protection Agency. Regulation of fuels and fuel additives. Notice of proposed rulemaking. Federal Register
13. Mahaffey KR, Annest JL, Roberts J, Murphy RS. National estimates of blood lead levels: United States 1976–1980: association of selected demographic and socioeconomic factors. N Engl J Med
14. Annest JL, Mahaffey KRNational Center for Health Statistics. Blood lead levels for persons ages 6 months–74 years, United States, 1976–1980. In: Vital and Health Statistics Series 11, No. 233. DHHS Pub. No. (PHS) 84-1683
. Washington, DC: Public Health Service; 1984.
15. Lustberg M, Silbergeld E. Blood lead levels and mortality. Arch Intern Med
16. Schober SE, Mirel LB, Graubard BI, Brody DJ, Flegal KM. Blood lead levels and death from all causes, cardiovascular disease, and cancer: results from the NHANES III mortality study. Environ Health Perspect
17. Menke A, Munter P, Batuman V, Silbergeld EK, Guallar E. Blood lead below 0.48 μmol/L (10 μg/dL) and mortality among US adults. J Am Heart Assoc
18. Lanphear BP, Rauch S, Auinger P, Allen RW, Hornung RW. Low-level lead exposure and mortality in US adults: a population-based cohort study. Lancet Public Health
19. Hu H, Shih R, Rothenberg S, Schwartz BS. The epidemiology of lead toxicity in adults: measuring dose and consideration of other methodologic issues. Environ Health Perspect
20. Weisskopf MG, Jain N, Huiling N, et al. A prospective study of bone lead concentration and death from all causes, cardiovascular diseases, and cancer in the Department of Veterans Affairs Normative Aging Study. Circulation
21. Weisskopf MG, Sparrow D, Hu H, Power MC. Biased exposure–health effect estimates from selection in cohort studies: are environmental studies at particular risk? Environ Health Perspect
22. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Lead
. Atlanta, GA: ATSDR; 2020.
23. Gerhardsson L, Hagmar L, Rylander L, Skerfving S. Mortality and cancer incidence among secondary lead smelters. Occup Environ Med
24. Steenland K, Barry V, Anttila A, et al. A cohort mortality study of lead-exposed workers in the USA, Finland and the UK. Occup Environ Med
25. Barry V, Steenland K. Lead exposure and mortality among US workers in a surveillance program: results from 10 additional years of follow-up. Environ Res
26. Centers for Disease Control and Prevention. Guidelines for the Identification and Management of Lead Exposure in Pregnant and Lactating Women
. Atlanta, GA: CDC; 2010.
27. Centers for Disease Control and Prevention. Blood Lead Reference Value
. Atlanta, GA: CDC; 2022. Available at: https://www.cdc.gov/nceh/lead/data/blood-lead-reference-value.htm
. Accessed December 9, 2022.
28. Cal/OSHA. California Occupational Safety and Health Administration. Draft Section 5198, Lead in General Industry, revised 11–11–2016. Available at: https://www.dir.ca.gov/dosh/doshreg/5198-meetings/draft-section-5198-revised-11-11-16.pdf
. Accessed December 9, 2022.
29. Cal/OSHA. California Occupational Safety and Health Administration. Draft Section 1532.1, Lead in Construction, revised 11–10–2016. Available at: https://www.dir.ca.gov/dosh/doshreg/5198-meetings/draft-section-1532.1-revised-11-10-16.pdf
. Accessed December 9, 2022.
30. OSHA. Occupational exposure to respirable crystalline silica. Fed Regist
31. Department of Occupational Safety and Health. Draft DOSH Lead Rule—June 2019
. Olympia, WA: Washington State Department of Labor & Industries; 2019. Available at: https://lni.wa.gov/safety-health/safety-rules/rulemaking-stakeholder-information/_leaddocs/LeadRule-WISHADraftLeadRule-June2019.pdf
. Accessed December 9, 2022.
32. NASEM. National Academies of Sciences, Engineering, and Medicine. Review of the Department of Defense Biokinetic Modeling Approach in Support of Establishing an Airborne Lead Exposure Limit
. Washington, DC: The National Academies Press; 2020.
33. Vork K, Carlisle J, Brown JP. Estimating Workplace Air and Worker Blood Lead Concentration Using an Updated Physiologically-Based Pharmacokinetic (PBPK) Model
. Sacramento, CA: Office of Environmental Health Hazard Assessment, California Environmental Protection Agency; 2013.
34. Vork KL, Carlisle JC. Evaluation and updates to the Leggett model for pharmacokinetic modeling of exposure to lead in the workplace. Part I: adjustments to the adult systemic model. J Occup Environ Hyg
35. Sweeney LM. Physiologically based pharmacokinetic modeling of airborne lead in support of development of an occupational exposure limit for Department of Defense Workers. US Department of Defense Final Technical Report. AFRL-SA-WP-TR-2019-0003. 2019.
36. Sweeney LM. Probabilistic pharmacokinetic modeling of airborne lead corresponding to toxicologically relevant blood lead levels in workers. Regul Toxicol Pharmacol
37. Roland-Holst D, Evans S, Neal S. Standardized Regulatory Impact Assessment: Revisions to Occupational Lead Standards
. Sacramento, CA: California Department of Industrial Relations; 2020.
38. Rudolph L, Sharp DS, Samuels S, Perkins C, Rosenberg J. Environmental and biological monitoring for lead exposure in California workplaces. Am J Public Health
39. Papanek PJ, Ward CE, Gilbert KM, Frangos SA. Occupational lead exposure in Los Angeles County: an occupational risk surveillance strategy. Am J Industr Med
40. Okun AH. The Monitoring Requirements of the OSHA General Industry Lead Standard Compliance Within Lead-Using Facilities [Dissertation]
. Chapel Hill, NC: University of North Carolina at Chapel Hill; 2000. Available from ProQuest #9993353.
41. Payne S, Jackson R, Materna B. Blood Lead Levels in California Workers: Data Reported to the Occupational Blood Lead Registry, 2012–2014
. Richmond, CA: California Department of Public Health, Occupational Health Branch; 2016.